The present invention relates to digital signal processing, and more particularly to automatic video signal identification for video test, for assurance of data present, or for generally translating a video waveform into a code to steer an appropriate measurement and/or an identifying text label.
Video signal detection involves many specific filters for feature extraction, including edge detection, chrominance demodulation and signal level detection, at various time intervals in a video horizontal line. To optimize this method it is necessary to Optimize both each feature filter and the weighing and/or the thresholding of the combination of the outputs of these filters for each signal to be identified. Implementation involves manually determining which filters should be used, where, and with what weightings and threshold for each signal to be identified. An example of this method is incorporated into the VM700 Video Measurement Test Set manufactured by Tektronix, Inc. of Wilsonville, Ore., United States of America.
Optimal signal detection, as described in Chapter 7 of "Modern Digital and Analog Communication Systems" 2d Ed. by B. P. Lathi published by Holt, Rinehart and Winston, Inc. (1989), uses cross-correlation, or equivalent matched filters, selection of maximum filter output, and a threshold to decide if a signal is present or not. The signal to be detected is either cross-correlated with a plurality of reference signals or is filtered using a plurality of matched filters, each designed with the time-reversed form of a corresponding one of the reference signals as its impulse response. This method was developed primarily to distinguish among signals which have a known amplitude and DC offset. This does not apply directly to identifying video signals because, while the gain of the synchronizing signal or color sub-carrier frequency may be set using an automatic gain control circuit and the DC offset of the back porch may be controlled with a clamp circuit, the various spectral and temporal components of the video are not always known relative to sync and burst. Also this method is very sensitive to changes in pedestal level, i.e., DC offset from back porch, on which other video may be added.
What is desired is a method of automatic video signal identification that is simple and robust while being adaptable.